Transformer



TRANS FORMER Filed Aug. 22, 1928 Fly].

INVENTOR Fred J Voye/ ATTbRNEY Patented Mar. '18, 1930 UNITED STATES PATENT OFFICE FRED J. VOGEL, O1 SHARON, PENNSYLVANIA, ASSIGNOB '10 WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY, A. CORPORATION OF PENNSYLVANIA TRANSFORMER Application filed August 22, 1828. Serial No. 301,288.

My invention relates generallyto transformers and particularly to the msulation thereof.

In the manufacture of transformers, it is the customary practice to mount the coils in such a way upon the core, that, when energized, one end of the coil will be at a greater voltage above the frame and core members than the other end. It is well known to those skilled in the art that an electrostatic field exists between the coils and the core of a transformer and when one end of the coils is at a greater voltage difference than the other end of the coils from the core and frame, the electrostatic field will be of varying intensity and will be of greater intensity where the voltage difference between the coil and core is greatest.

It has been found that the most concentrated section of the electrostatic field is located near the corners of the coil, where a very non-uniform distribution of electrostatic flux exists, and it is the greater intensity of fiux at this section which determines the clearance or thickness of dielectric between the coil and the core members. My invention provides a method of more uniformly distributing the dielectric flux between the coils and core of the transformer, thus reducing its value at the corners, and thereby permitting a reduction in the clearance space between the coils and the core of the transformer.

The object of my invention, generally stated, is to provide a method of insulating transformer coils from the core on which they are mounted.

A further object of my invention is to provide a method of uniformly distributing the dielectric flux between the core and windings of the transformer.

A more specific object of my invention is to provide a method of obtaining a uniform distribution of dielectric flux between the corners of a transformer coil and the core upon which it is mounted.

Another object of my inventlon is to provide a method of reducing the clearance space between the core and coils of the transformer.

Other objects of my invention will become aplparent to those skilled in the art when the fo owing description is considered in conjunction with the accompanying drawings in which:

Figure 1 is a sectional view in front elevation of a transformer core with the windings mounted thereon and insulated in accordance with my invention;

Fig. 2 is a sectional view of a corner of a transformer insulated in the usual manner, showing diagrammatically the core and coils and the distribution of the dielectric field therebetween Fig. 3 is a view, corresponding to that in Fig. 2, of a transformer insulated in accordance with my invention and showing the uniform distribution of dielectric flux.

Referring now to Fig. 1, a shell-type core member 10 is provided and a plurality of windings 11 are wound thereon. In accordance with the conventional design, a thin layer of insulating material 12 is interposed between the core 10 and the windings 11 on the inside, whereas, a clearance space 13 is left between the high and low voltage windings and the outer periphery of the windings 11 and the core 10. The clearance spaces 13 may be filled with oil in case of an oil-immersed transformer or may be open to the free circulation of air or any other fluid. In any event, however, the medium with which the clearance spaces 13 are filled will constitute a dielectric between the windings 11 and the core 10.

In the operation of transformers such as those to which my invention relates, and illustrated in the drawings, it is the usual practice to connect the core'member 10 to ground. Furthermore, it often occurs that one end of the coil of windings 11 is also grounded, and the embodiment shown in Fig. 1 is applicable when the lower end of the windings 11 is to be grounded. Since the lower end of the windings 11 is at the same potential as the core member 10, when grounded, there will be no electrostatic field between the lowermost point of the windings 11 and the core 10, but since the voltage in the windings 11 increases to a maximum value at the uppermost winding, an electrostatic field will exist, and its intensity will vary substantially uniformly along the length of the windings 11. The clearance space 13 must, therefore, be of suflicientwidth to prevent a breakdown in the dielectric between the windings 11 andthe core 10 at the'point of maximum intensit A diagram showing the distribution 0 dielectric flux and an equi-potential line a-b in the electrostatic'field between the corners points about the corner such as 0, Whereas at the other points such as d, the potential gradient is of a'lesser value. It will be seen that the points 0 on the line a-b, where the dielectric flux is most concentrated, are the points of maximum voltage gradient, where as the points d, where the dielectric flux is more thinly distributed and along the portion of the windings 11 adjacent to the corner, represent a point of low voltage gradient, so that the point at is not involved in the probl m of reducing the clearance 13 between the windings 11 and the core 10.

I have provided a layer of solid insulation 14 which has a relatively high specific inductive capacity as compared to the medium in the clearance space 13 and this layer of insulation is disposed upon the end of the coil 11 which has the greatest potential difference from the core 10. It has been found that a layer of insulation having high specific inductive capacity disposed upon a coil, as I have indicated, efiects an even distribution of the dielectric flux about the corner of the winding, as shown in Fig. 3. When the dielectric flux between the windings 11 and the core 10 is distributed in the uniform manner shown in Fig. 3, an equi-potential line such as a'-b represents a uniform voltage gradient about the corners and thereby eliminates the dangerous points of high voltage gradient illustrated at the points 0 of Fig. 2. When the points of high voltage gradient have been eliminated, it is possible to reduce the clearance 13 to a value whichwill be determined by the reduced maximum concentration of dielectric flux along the side of the windings 11.

It is, therefore, possible, by the introduction of a layer of insulation having a high specific inductive capacity on one side of a transformer coil to reduce the clearance or thickness of dielectric on an adjacent side without increasing the dielectric stress in the medium interposed between the windings 11 and the core 10 of the transformer.

Since it will be possible to modify the embodiment hereinbeforeset forth in various ways without departing from the spirit and scope of the invention it is desired that the foregoing description be construed as merely illustrative and not ina limiting sense.

I claim as my invention 1. A transformer having a core, windings disposed upon said core and s aced therefrom causing an electrostatic eld to exist between said core and windings, the intensity of said electrostatic field varyin uniformly as the length of the windings an means for shaping the electrostatic field at the angle of the winding structure comprising a layer of insulation disposed upon the end of said windings at which the electrostatic field is most intense, said insulation having a higher specific inductive capacity than the medium of the space between the core and windings, whereby said space may be reduced to a minimum.

2. A transformer comprising a core, a winding disposed upon said core, causing an electrostatic field of varying intensity between said core and winding, a dielectric medium between said core and winding, a layer of insulation, having a specific inductive capacity higher than that of the dielectric medium, disposed at the angle of the winding structure, thereby reducing the dielectric stress adjacent the end of the winding.

3. Atransformer having a core and windings spaced therefrom, causing an electrostatic field in said space, and means for uniformly distributing the dielectric flux at the high-potential angleof the winding structure by the application of insulation having a high specific inductive capacity adjacent said angle, whereby the space between the core and windings may be reduced.

In testimony whereof, I have hereunto subscribed my name this 16th day of August FRED J VOGEL. 

